Process and apparatus for electrolytically treating metal tubes



Feb. 25, 1969 wElNREmH 3,429,787

PROCESS AND APPARATUS FOR ELECTROLYTICALLY TREATING METAL TUBES FiledJune 15, 196% Sheet or 4 FIG. /5

INVENTQR BY Mel/1M MM J,

ATTORNEY Feb. 25, 1969 W. WEINREICH PROCESS AND APPARATUS FORELECTROLYTICALLY TREATING METAL TUBES Filed June 15, 1964 FIG. 3

Sheet 2 of4 inllliillzlulzAw ivlilllllllllllllllllI'll/In \wllnl IIIII!Mllllllllllllllgg. i

INVENTOR PROCESS AND APPARATUS FOR ELECTROLYTICALLY TREATING METAL TUBESFeb. 25, 1969 w. WEINREICH 3,429,787

PROCESS AND APPARATUS FOR ELECTROLYTICALLY TREATING METAL TUBES FiledJune 15, 1964 Sheet 4 of 4 FIG. 5

INVENTOR 15/6. [inrefz 4.

ATTORNEY United States Patent 3,429,787 PROCESS AND APPARATUS FORELECTRO- LYTICALLY TREATIN G METAL TUBES Wolfgang Weinreich, Paderborn,Germany, assignor to Benteler-Werke A.G. Werk Neuhaus, Paderborn,Germany Filed June 15, 1964, Ser. No. 375,116 Claims priority,application Germany, June 18, 1963, B 72,320 US. Cl. 20426 12 ClaimsInt. Cl. C23b /56 ABSTRACT OF THE DISCLOSURE A process forelectrolytically depositing on the interior and exterior surfaces ofelongated metal tubes a metal coating while passing the tubessuccessively through an electrolytic bath in which an elongatedconductor located in the bath passes coaxially through the tubes withouttouching the latter, in which a metal anode is located in the bath whilethe tubes are connected as cathodes and in which the tubes are advancedthrough the bath in such a manner as to maintain at all times one-halfto one-third of the conductor uncovered so that the conductor will havea dipole function receiving metal from the anode while the conductor isuncovered by a tube and giving up the metal thus received from the anodeto the interior surface of the tube while the conductor is coveredthereby, and an apparatus for carrying out the process.

The present invention relates to the electrolytic treatment of articles.

More particularly, the present invention relates to the electrolytictreatment of elongated metal tubes.

It is already known to electrolytically deposit on the inner surfaces ofelongated metal tubes, which may have an inner diameter small asapproximately 3 mm., metals such as zinc, copper, cadmium, or the like,while continuously advancing the tubes one after the other through theapparatus. The tubes are transported along a generally horizontal pathand are connected into an electrical circuit in such a way that thetubes themselves form the cathode while there is maintained in theinterior of the tubes an elongated conductor in the form of a wire whichacts as an anode, and with such an apparatus the tubes are successivelyadvanced through several treating baths in one of which of course themetal coating will be electrolytically deposited on the inner surface ofthe tubes. The elongated wire which passes coaxially through theinteriors of the several tubes as they are advanced through the severaltreating baths may carry a plurality of plugs which act in the manner ofpistons in that they slidably engage the interior surfaces of the tubesas they are transported through the apparatus, and these plugs are madeof plastic or other electrically non-conductive material, and theyresult in positively sucking the treating liquids into the tubes andpositively displacing the treating liquid out of the tubes as they arecontinuously advanced through the apparatus, so that in this way theplugs provide a pumping action to guarantee thorough contact of thetubes with the treating liquids. With an apparatus of this type it ispossible to achieve a practically uninterrupted coating on the innersurfaces of relatively long tubes even if they are of relatively smallinner diameter. This known apparatus and process is highly economicaland have the advantage of providing exceedingly uniform coatings on themetal tubes. Moreover, the plugs by providing the above-mentionedpumping action guarantee complete flooding of the surfaces of the tubeswith treating liquids while also guaranteeing that 3,429,787 PatentedFeb. 25, 1969 "ice there is no undesired intermixing of the severaldiiferent treating liquids.

Of course, it is essential with an apparatus of the above type tomaintain the inner conductor connected into the electrical circuit sothat it will act as an anode, even when the tubes are initiallyintroduced into the apparatus with the conductor extending coaxiallyinto the interiors of the tubes, so that special switch assemblies arerequired which will provide at one place a switch which opens in orderto permit a tube to be introduced into the apparatus whilesimultaneously a second switch closes so as to maintain the innerconductor connected in the circuit, and then when a tube has beenstarted through the apparatus the first switch closes and the secondswitch automatically opens, and with such a known switching arrangementit is possible to maintain the inner conductor connected in theelectrical circuit so that it will uninterruptedly act as an anode.

Of course, it is also possible to provide electrolytic coatings on theexterior surfaces of the tubes by locating in the electrolyte metalelectrodes made of a metal which is to be deposited on the exteriorsurfaces of the tubes and these electrodes are also connected into thecircuit so that they will act as anodes. The above principle can also beused for electrolytically treating metals Without depositing coatingsthereon. For example, the above principle may be used in electrolyticdegreasing or polishing of tubes. In order to polish the tubes it isonly necessary to reverse the polarity so that the tubes become theanodes and the inner and outer electrodes become the cathodes.

Although the above-discussed method and apparatus for continuouslytreating both the inner and the outer surfaces of elongated metal tubesis extremely simple and quite practical, there is a disadvantage notonly in the necessity of providing a complex switching arrangement asdiscussed above but also in the fact that during deposition of a coatingon the inner surfaces of the tubes it is necessary to replenish theinner anode from time to time, and particularly when dealing with tubesof small inner diameters this requirement is extremely inconvenientsince it requires a long period of time and is of considerabledisadvantage. The smaller the inner diameter of the tube the more timeis required for replenishing the inner anode. The reason for this isthat the thickness of the inner anode which is surrounded by the tube asit passes through the electrolyte is of necessity smaller with tubes ofsmaller inner diameters, so that when dealing with tubes of relativelysmall inner diameters the anodes become consumed at a faster rate.

It has already been proposed to alleviate this latter problem byproviding anodes in the form of suitable sleeves which are mounted on aconductive core made of copper wire, for example, but with theconvenience of simply slipping sleeves onto a copper Wire there goes thedisadvantage of a smaller time between the periods of when the anodemust be replenished while on the other hand there is always the dangerthat after the sleeve has become consumed the copper core itself willbecome consumed and can lead to undesired breakage of the copper core inthe electrolytic bath. Thus, while there are indeed certain advantagesfrom a known method and apparatus of the above type, as compared tostructures where tubes are maintained stationary While they are treated,nevertheless particularly when dealing with tubes of small innerdiameters, the advantages which can be achieved are greatly diminishedby the requirement of frequent replenishing of the anode.

It is accordingly a primary object of the present invention to provide amethod and apparatus of the above general type which will make itpossible to completely avoid the necessity of replenishing the anodefrom time to time.

In particular, it is an object of the present invention to provideelectrolytic deposition of a suitable metallic coating on the interiorand exterior surfaces of elongated metal tubes, particularly tubes ofrelatively small diameter, while obtaining the metal coating solely froma plate which is situated at the exterior of the metal tubes in theelectrolytic bath so that. while such a plate will of course be consumedat a rate which is faster than in conventional electrolytic processesand apparatus, nevertheless since the plate can be made quite thick andcan be easily replaced the elimination of the necessity for replenishingthe inner electrode provides a great advance in the art.

It is furthermore an object of the present invention to provide a methodand apparatus of the above type which makes it possible to provide thedesired coatings of the desired quality on the metal tubes from the verybeginning of the operation so that the first tube is coated aseffectively as all of the subsequent tubes while at the same timeautomatically compensating for variations in the operations resultingfrom variations in the distances maintained between the successive tubesas well as variations in the concentration of the electrolyte, etc.

It is also an object of the present invention to provide the aboveadvantages achieved with the present invention not only for the coatingof tubes but also for other electrolytic processes such as the polishingof coated tubes.

It is also an object of the invention to provide a process and apparatusof the above type which makes it possible to provide a predeterminedrelationship between the thicknesses of the coatings deposited on theexterior and interior of metal tubes.

It is furthermore an object of the present invention to provide aprocess and apparatus according to which a plurality of metal tubes canbe treated simultaneously with a structure where a series of treatingbaths are arranged one after the other with a transporting structure forefficiently transporting the tubes successively through the severalbaths while at the same time maintaining the liquids particularly of theelectrolytic bath circulating between a reservoir and a containerthrough which the tubes pass while compensating for any leakage whichmay occur and While at the same time providing an efficient electricalstructure for maintaining the desired electrical circuit with thevarious parts which are to act as anodes and cathodes maintained at theproper polarities.

With the above objects in view the invention includes, in a process forelectrolytically treating elongated metal tubes which are advancedthrough an electrolytic bath in which there is located an elongatedconductor which is not connected to any source of current and whichpasses coaxially through the tubes without contacting the latter as theyare advanced through the electrolytic bath while there is alsomaintained in the electrolytic bath a plate of a suitable metal fromwhich the metal for the coatings is derived, the step of advancing thetubes successively through the electrolytic bath while maintainingbetween the tubes a spacing which will uncover at any one timepreferably one half of the electrical conductor which is in theelectrolytic bath but at a maximum not more than two-thirds of thiselectrical conductor.

Also, the invention includes, in an apparatus for electrolyticallytreating elongated metal tubes, an electrolytic bath means adapted tocontain an electrolyte and carrying an elongated conductor which extendsthrough the electrolyte and which is not connected to any source ofcurrent. A transporting means transports the metal tubes through thebath one after the other with the conductor extending coaxially throughbut not contacting the metal tubes, and a metal plate which is in theelectrolyte is connected electrically with the metal tubes to a sourceof direct current which provides for the metal tubes, on the one hand,and the plate, on the other hand, opposite polarities.

Thus, according to the process of the invention, there is provided anelectrolytic bath through which the elongated metal tubes aresuccessively advanced one after the other. An elongated metal electricalconductor, in the form of a suitable wire, for example, is maintained inthe electrolyte and in accordance with the invention is not connected toany source of current so that the problem of providing a switchingarrangement for connecting the conductor to a source of current iseliminated. The tubes are successively advanced through the electrolytewith this elongated conductor extending coaxially through the interiorsof the tubes without contacting the latter, and a metal plate issituated in the electrolyte and connected electrically with the tubes insuch a Way that, for the purpose of deposition of coatings on theinterior and exterior surfaces of the tubes, this metal plate acts as ananode while the tubes themselves act as cathodes. According to theprocess of the invention the tubes successively transported through theelectrolyte are advanced in such a way that not more than two-thirds ofthe electrical conductor is covered by the tubes at any one time, andpreferably one half of the electrical conductor remains uncovered at alltimes, which is to say the spacing between the successive tubes ideallywill be such that the distance between the successive tubes will beequal to the lengths of the tubes themselves.

In order to appreciate how the results of the invention are achieved, itis necessary to take into consideration the following explanation:

Assuming that the electrolyte is Zinc sulfate and contains an anode inthe form of a metal plate of zinc as Well as a cathode made of iron,with the anode and cathode provided with current through suitablemetallic conductors and a suitable source of current, then in themetallic conductors at the exterior of the electrolyte, assuming thatthere is a sufficiently high voltage, there will be a flow of electronsfrom the anode to the cathode. Simultaneously there will be in theelectrolyte as a result of the applied voltage the formation of ionizedzinc atoms at the anode which go into the solution as doubly chargedpositive zinc ions, and as a result of the diffusion and voltage dropthey wander off into the electrolyte While at the cathode the zinc ions,as a result of diffusion as well as the voltage drop, are neutralized bythe negative charge resulting from the presence of the electrons, andthus metallic Zinc is deposited at the cathode. Thus, as a result withthis known process there will be within the electrolyte a transportationof ions from the anode to the cathode and a transportation of electronsin the reverse direction. If an ammeter is connected to the metallicconductors at the exterior of the electrolyte than the flow of electronscan be shown by the ammeter, the magnitude of the current beingdetermined on the one hand by the applied voltage as well as theelectrical resistance of the metallic conductors and on th other handfrom the inner resistance of the electrolyte. This inner resistance ofthe electrolyte will depend upon, among other things, the size of theexposed electrode surfaces and the speed of diifusion of the zinc ions.

Assuming now that the relatively high internal resistance of the zincsulfate electrolyte, as compared to metallic zinc, is reduced byintroducing into the electrolyte a metallic conductor of a metal such aszinc, for example, then this conductor will have the character of adipole, and the above-described process will then take place in a mannersimilar to the operations which occur when a pair of cells, eachincluding an anode and a cathode, are connected together in series. Inother words 'when a zinc conductor, in the above exemaple, is introducedinto the electrolyte, it acts as a dipole in that the negative pole ofthe zinc conductor in the electrolyte will have deposited thereon zincfrom the zinc anode plate, while the positive pole of the zinc conductorwhich has been introduced into the electrolyte will act as an anode withrespect to the iron cathode and zinc will flow from the positive pole ofthe dipole zinc member to the iron cathode to be deposited thereon.

The above principle is used in the process and appa ratus of theinvention by providing the inner electrical conductor which is notconnected to any source of current but which extends through theelectrolyte and which extends coaxially through the metal tubes withoutcontacting the latter as the metal tubes are advanced through theelectrolyte. With the invent-ion there is of course an anode located inthe electrolyte at the exterior of the metal tubes, and the elongatedconductor in the interior of the metal tubes acts as a dipole in themanner described above. Thus, although it is not connected to any sourceof current, when the inner conductor is not covered by the metal tube itacts as a negative pole and there is deposited upon the conductor metalfrom the anode in the electrolyte at the exterior of the metal tube,while when the conductor is covered by the metal tube the coatingpreviously deposited on the conductor for the anode will flow from theconductor to the interior surface of the metal tube. Of course, it isassumed that the metal tube is electrically connected into the circuitas the cathode, and in addition it must be assumed that there is noelectrical circuitry which will disturb the dipole function of the innerconductor or which will interrupt this function and also the anode platewhich is in the electrolyte and the metal tube which is coatedrespectively form the anode and cathode of an electrical circuit whichis provided with a source of direct current. In other words the metaltubes are electrically connected to the negative pole of the source ofdirect current while the anode plate is connected to the positive poleof the source of direct current.

Of course, ideally the successive metal tubes should be spaced from eachother by a distance equal to their length, so that in this way one halfof the inner electrical conductor which has the dipole function isuncovered and thus there is an equal opportunity for metal to becomedeposited on the inner conductor when it is uncovered and for the metalto flow from the inner conductor to the inner surface of the metaltubes. However, the proces. and apparatus of the invention function verywell even if two thirds of the inner conductor remains covered so thatonly one third thereof is uncovered at any given time, the onlydifference being in that this latter case the exterior surface of themetal tube will receive a somewhat thicker coating than the interiorsurface thereof. Moreover, the inner conductor which may be made ofcopper, for example, can initially be provided with sleeves of zincmounted thereon, so that in this way there is an initial resenve ofmetal to be deposited on the inner surface of the metal tubes and inaddition such a reserve of metal will automatically compensate forvariations in the lengths of the tubes and the distances therebetween aswell as in the concentration of the electrolyte, etc. However, it willbe seen that with the invention it becomes completely unnecessary toreplenish the anode in the interior of the metal tubes from time totime. Because the outer anode plate supplies the metal for the interioras well as the exterior coating, relatively long periods will elapsebefore it is necessary to change the exterior metal plate which in anyevent is very quickly and easily changed, and the necessity of changingeither the inner conductor or mounting new sleeves thereon to replaceconsumed sleeves is completely avoided with the process and apparatus ofthe invention.

Of course, the process and apparatus of the invention can be used forpolishing an already coated tube simply by reversing the polarity sothat the coated tube is the anode and the plate becomes the cathode.

Of course, in order to guarantee that at least one third of the innerconductor remains uncovered at all times it is necessary for the innerconductor to be longer than the metal tubes on which the coating is tobe electrolytically deposited. Ideally the inner conductor will ofcourse be twice as long as the metal tubes so that at all times one halfof the conductor is exposed.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

FIG. 1A and FIG. 1B, which is a continuation of the right end of FIG.1A, schematically illustrate the entire installation forelectrolytically treating the elongated metal tubes;

FIG. 2 schematically illustrates on an enlarged scale, as compared toFIGS. 1A and 1B, that part of the installation which includes theelectrolytic baths in which the metal is electrolytically deposited onthe metallic tubes;

FIG. 3 is a longitudinal sectional view, on a scale which is stillfurther enlarged as compared to FIG. 2, fragmentarily illustrating themanner in which a metal tube is transported with the inner conductorpassing coaxially therethrough;

FIG. 4 is a sectional schematic elevation showing details of theelectrolytic bath and structure associated therewith; and

FIG. 5 is a transverse end view of the electrolytic structure of FIG. 4.

The entire installation which is shown in FIGS. 1A and 1B includes aplurality of individual units and containers arranged one after theother in the direction of movement of the tubes 1 and adapted to containthe various treating liquids for treating the tubes prior to theelectrolytic treatment thereof for depositing metal thereon, forexample, as well as for treating the tubes subsequently to theelectrolytic deposition of metals thereon. The first unit in thedirection of movement x of the tubes is the table 2 on which the severaltubes are arranged beside each other so as to move simultaneouslythrough the apparatus. Next to the table 2 is located the transportingunit 3 which is provided with a plurality of pairs of rollers 3a and 3bdriven in any suitable way and adjustable to the diameter of theparticular tubes, the pairs of rollers 3a and 3b equalling the number oftubes and engaging the latter to transport the tubes in the direction ofthe arrow x. A bath 4 follows the transporting unit 3, and this bathcontains a known degreasing solution for preliminarily degreasing thetubes as they move through the bath 4. Subsequent to the bath 4 is afurther treating container 5 which in a known way electrolyticallydegreases the tubes. At 5a there is indicated a container whichimmediately follows the electrolytic degreasing bath 5 and which issimply a water bath for the purpose of washing the tubes as they advanceout of the bath 5 and through the bath 5a. Then the tubes are engaged bya further transporting unit 6 which may be constructed identically withtransporting unit 3 and which has a plurality of pairs of rollers 6a and6b for respectively engaging and continuing the movement of the tubes 1through the apparatus to the pickling bath 7 where the tubes aredescaled with a suitable pickling solution which may be, for example,10% sulfuric acid solution.

The treating bath 7 is followed by a further transporting unit 8 whichis provided with a plurality of pairs of rollers 8a and 8b which on theone hand serve to continue to transport the tubes in the same way as therollers of the other transporting units and which on the other hand areelectrically conductive and are connected into the electrical circuit soas to supply cathode current for the tubes 1. For this purpose therollers 8a and 8b are engaged by electrically conductive slip contactswhich are not illustrated in the drawing and which are electricallyconnected with a copper bus bar 9a which is connected to the negativepole of a source of direct current which is not illustrated in thedrawing.

Subsequent to the electrically conductive transporting means 8 islocated a bath means 10a, 10b which is the electrolytic bath means inwhich the metal coating is electrolytically deposited on the inner andouter surfaces of the tubes, and in accordance with one of the featuresof the invention this bath means is divided into a pair of electrolyticbath units 10a and 10b. After passing through the electrolytic bath unit10a the tubes are engaged by a further transporting unit 11 providedwith a plurality of pairs of rollers 11a and 11b which engage andcontinue the transportation of the tubes 1. The transporting means 11 isalso electrically conductive, and the rollers 11a and 11b are engagedalso by unillustrated slip contacts which are electrically connectedwith a bus bar 912 which is also connected to the negative pole of thesource of direct current so that the connection of the tubes into thecircuit so as to form cathodes is maintained by the transporting means11.

Referring now to FIG. 1B which forms a continuation of FIG. 1A, it willbe seen that there is located immediately subsequent to the transportingunit 11 a transporting unit 12 which is provided with the pairs ofrollers 12a and 12b for engaging and continuing the transportation ofthe tubes 1, and these rollers are also engaged by unillustrated slipcontacts which are electrically connected with the bus bar 90 which isin turn connected to the negative pole of the source of direct current,so that the negative polarity of the tubes is maintained by thetransporting unit 12.

Immediately subsequent to the transporting unit 12 is located the secondbath unit 10b of the electrolytic bath means, and this bath means 10b isfollowed by a further transporting unit 13 provided with pairs ofrollers 13a and 13b for engaging and continuing the transportation ofthe tubes, and these rollers also are engaged by slip contacts which areelectrically connected with a bus bar 9d, and again this latter bus baris connected to the negative pole of the source of current so that thenegative polarity of the tubes is still maintained by the transportingunit 13.

The conducting of the anode current to the electrolytic bath means 10a,10b, and in particular to the metal electrodes 14a, 14b, 14c and 14dlocated in the electrolytic baths and being in the illustrated examplezinc plates, can take place also by copper bus bars, these bus bars 15aand 1517 both being electrically connected to the positive pole of thesource of direct current which is not illustrated in the drawings. Theelectrolytic baths 10a and 1017 which are filled with zinc sulfate arefollowed by a pair of passivation baths 16 and 17 which contain amongother things chromic acid and which are immediately preceded,respectively, by water baths 16a and 17a. The passivation baths 16 and17 are followed by a further transporting unit 18 provided with thepairs of rollers 18a and 1812 which engage and continue thetransportation of the tubes 1 and which serve to deliver them to thedischarge table 19.

The pair of electrolyte containers 10a and 10b are shown on an enlargedscale in FIG. 2, partly in section, while FIG. 3 shows on a furtherenlarged scale the structure of the inner anode assembly.

Throughout the entire length of the entire installation shown in FIGS.1A and 1B there are arranged a plurality of elongated conductors 20, inthe form of wires, the number of which are equal to the number of tubes1 which are arranged beside each other and which move simultaneouslythrough the apparatus so that each tube 1 will have this elongatedconductor passing coaxially therethrough as the tube 1 is advancedthrough the installation. The elongated conductors 20 have an exteriordiameter substantially smaller than the inner diameter of the tubes,this latter inner diameter being as small as three or four millimetersfor example, so that the wires 20 of course have a relatively smalldiameter. With the exception of the portions of each wire 20 which passthrough the bath 5 and the electrolytic baths 10a and 10b, each wire 20has the construction shown at the left of FIG. 3, namely an inner core20a made of metal and surrounded by a covering of plastic 20b, which isof course electrically non-conductive. Inasmuch as the electrolyticbaths 10a and 10b and the bath 5 form a minor fraction of the totallength of the installation shown in FIGS. 1A and 1B, it is clear thatthe wire 20 for the most part has this construction according to whichit is in the form of an inner metal wire 20a surrounded by a plasticcoating 20b.

In the degreasing bath -5 which electrolytically degreases the tubeseach of the wires 20 is composed Only of the inner portion 20a, theplastic covering 20b being omitted in the bath 5, so that the bare wire20a is uncovered and exposed in the electrolytic degreasing bath 5, andthis uncovered portion of the wire is connected by suitable contacts tothe anode current so that the degreasing can be carried out in anelectrolytical manner.

In the electrolytic baths 10a and 10b the structure of the innerconductor changes in that in these baths there is also located anelectrical conductor, but not an electrical conductor covered by acoating of insulation. Instead there extends through the baths 10a and10b a copper core 21 which is surrounded by a plurality of rigid metalsleeves 22 made of zinc, and the copper wire portion 21 of the wire '20in the baths 10a and 10b is not supplied with any current and is notconnected into any circuit so that it can perform the above-describeddipole function in the electrolytic baths, enabling the wire 21 to haveat one time the function of a cathode with respect to the exterioranodes 14 and at another time to have the function of an anode withrespect to the tubes 1 which surround the conductor 21. For this purposethe wire portion 21 of each wire 20* is in the form of a completelyseparate and independent insert introduced into the length of the wire20 at a suitable interruption in the portion 20a thereof, and thisinsert 21 for each wire 20 is independent of the remainder of the wire20' and is separately mounted and interchangeable, and in addition it isinsulated from the remainder of the wire 20 as by being connectedthereto by way of sleeves 23 (FIG. 3) made of any suitable electricallynon-conductive material such as a suitable plastic, rubber, or the like.The exposed portion of the wire which is in the degreasing bath 5 isalso separate from the remainder of the wire 20 and connected thereto bysuitable insulating sleeves, but of course this exposed wire portion ofeach wire 20 in the bath 5 is supplied with current from the exterior bythe anode conductors.

As is apparent particularly from FIG. 3, the core 21 carries between theseveral zinc sleeves 22 the plugs 24 which act similarly to pistons andwhich have a frustoconical configuration, these plugs 24 being made ofany suitable resilient, elastically deformable plastic, and plugs havetheir largest outer diameter slightly greater than the inner diameter ofthe tubes 1 so that they can perform a piston-like sealing function atthe interior of the tubes 1 which move along the conductors,respectively, with the latter passing coaxially through the tubes 1.These plugs in addition serve simultaneously for centering theconductors in the interior of the tubes so that in this way they promotethe efficient deposition of a metal coating on the inner surfaces of thetubes. The plugs 24 are rigidly fixed to and immovable with respect towire core 21 and they are additionally provided on the wire 20 at everycontainer of the installation in the region of the entrance anddischarge of the tubes into and out of the several containers, so thatonly in the electrolytic deposition baths 10a and 10b as well as in theelectrolytic degreasing bath 5 are there additional plugs so as toprovide in these baths the centering of the anode wire with respect tothe interiors of the tubes, and thus in these baths even a very slightsagging of the inner conductor will be reliably prevented.

The several baths through which the tubes successively pass while movingalong the installation shown in FIGS. 1A and 1B are identicallyconstructed, and thus the details of only one of these baths areillustrated in FIGS.

9 4 and 5 where by way of example the detailed structure of theelectrolytic bath a is illustrated.

Thus, it will be seen that each of the baths includes a frame whichcarries a lower container or reservoir 26 which has an open top, whichis of a relatively large size, and which contains the treating liquid ofthe particular bath, in this case the electrolyte. As is apparent fromthe lower portions of FIGS. 4 and 5, a pipe 27 provides communicationbetween the lower interior of the reservoir 26 and a motor-driven pump28 which sucks the treating liquid out of the reservoir 26, and a pipeis connected to the outlet of the pump 28, this pump 30 carrying a valve29 and having an upper outlet end 30a through which the treating liquidis discharged into an upper container 31 which is shallower than thereservoir 26 and in which the actual treatment of the tubes 1 takesplace.

As is shown most clearly in FIG. 4, the interior of the container 31 ofthe bath 10a, and of course also of the bath 10b, accommodates theexterior anode plates, and thus the exterior anode plates 14a and 14bare shown in FIG. 4 in the interior of the container 31. Moreover, thecontainer 31 is limited by a pair of end walls 32a and 3212 throughwhich the tubes 1 pass at an elevation lower than the liquid level y ofthe treating liquid. For this purpose the end wall 32a is provided witha row of openings 33a, through which the several tubes 1 respectivelypass into the bath 31, and the wall 32b is provided with a row ofopenings 3311- through which the tubes move out of the treating bath 31,and each of these entrance and discharge openings 33a and 33b isprovided with a suitable sealing ring which extends along the edge ofeach opening and which engages the exterior surface of the tube in asubstantially fluid-tight manner, so that in this Way discharge of thetreating liquid into the liquid-collecting chambers 34a and 34b situateddirectly before and after the container 31 is very greatly reduced. Acertain steady leakage of the treating liquid does take place into theoverflow chambers 34a and 34b which are respectively provided withopenings 35a and 35b through which the tubes also pass and these latteropenings are also provided with suitable sealing rings which slidablyengage the exterior surface of the tubes. The overflow collectingchambers 34a and 34b communicate with conduits 36a and 36b, respectivelywhich direct the excess treating liquid back into the reservoir 26, sothat in this way the liquid level in the interiors of the overflowchambers 34a and 34b are always at an elevation lower than the inlet andoutlet openings 35a and 3511.

In the region of each entrance opening 33a and discharge opening 33b ofeach container 31 a plug 24 is located so that as the leading open endof each tube enters into a particular container the plug 24 in the tubewill suck the treating fluid into each tube so as to reliably fill thelatter with the treating fluid while at the same time reliablypreventing the several treating fluids from becoming mixed with eachother, and as the trailing end of each tube moves beyond the plug 24 atthe entrance opening of the particular bath the plug 24 at the dischargeopening will guarantee that the treating liquid in each tube is reliablydisplaced out of the latter, so that in this way the plugs also serve tosuck the treating fluids into and displace the treating fluids out ofthe several tubes to guarantee intimate contact between the inner tubesurfaces and the treating liquids.

As is particularly apparent from FIG. 5, the width of the installation,from front to rear, is great enough so that, in the illustrated example,twelve tubes 1 can be arranged beside each other on the entrance table 2and can simultaneously move through the installation. It is of courseimmaterial to the operation how many tubes are arranged beside eachother so as to move simultaneously through the apparatus, but in theillustrated example there will be groups of twelve tubes moving atpredetermined intervals one after the other through the apparatus, andin addition it is immaterial whether all twelve tubes are aligned witheach other so as to receive the same treatments during precisely thesame time intervals. In other words as long as a series of tubes aretransported at predetermined intervals along a given conductor, it makesno difference whether the movement of tubes along one conductor issynchronized with the movement of tubes along another conductor. Thus,the several tubes which move along several conductors can have anydesired relationship with respect to each other. The several conductorswhich are arranged across the installation operate completelyindependently of each other. Thus, each conductor in the electrolyticbaths 10a and 10b, for example, must have at least one third of itslength uncovered at any one time, as pointed out above, but since theseveral conductors 21 operate completely independently of each otherwith their particular polarity of any instant determined by whichportion of a given conductor 21 is surrounded by a tube 1, it is clearthat it is immaterial whether the several tubes 1 move with anyparticular synchronization along the several conductors.

The electrolytic bath means 10a, 10b will have a single continuousconductor 21 passing therethrough and insulated from the remainder ofthe wire 20, as described above, and it is preferred to have a pair ofseparate baths 10a and 10b than a single continuous bath, since in thisWay the length of each bath and of course the portion of the conductor21 located therein can correspond to the length of a tube 1, and thus inthis way in one bath the conductor 21 will be completely uncovered at agiven time, as shown in the bath 10b in FIG. 2, so that according to thedipole function the deposition of metal from the plates 14c and 14d cantake place on the portion of the conductor in the bath 10b while as thetube 1 advances into and through the bath 10b the dipole function willcause the metal to then be transferred from the conductor onto the innersurface of the tube 1 while the conductor in the bath 10a now becomesprogressively uncovered to an increasing extent so as to receive metalfrom the plates 14a and 14b in the bath 10a.

Remembering that ideally the spacing between the tubes will be equal tothe lengths of the tubes, then where each of the baths 10a and 10b has alength corresponding to that of the tubes, it is clear that one tubewill be completely located in the bath 10b before the next tube entersinto the bath 10a, and on the other hand a tube will have been entirelytransported out of the bath 10b before the next tube enters into thebath, so that in this way the required extent of uncovering of the innerconductor can be maintained.

With the ideal arrangement shown in FIG. 2 and according to which thespacing between the tubes equals their lengths and the tubes are equalto the lengths of the baths 10a, on the one hand, and 10b, on the otherhand, there will be practically no consumption of the zinc sleeves 22inasmuch as according to the dipole function precisely the amount ofmetal deposited on the inner conductor from the anode plates will beremoved therefrom to be deposited from the inner surfaces of the tubes.

Of course, the number of electrolytic baths can be increased to anynumber in the interest of enlarging the entire length of the regionwhere electrolytic position takes place, the only requirement being thatthe total length of the tubes is not greater than two thirds of thetotal length of the inner conductor which has the dipole function, andpreferably the tube sholud only be one half of this length, as pointedout above. Otherwise, the enlarging of the effective length of theinstallation along which electrolytic deposition takes place, which isto say elongating the electrolytic baths with respect to the lengths ofthe tubes, makes it possible to increase the speed with which the tubesare moved through the installation Without undesirably influencing thequality of the deposition of the zinc coating on the inner and outersurfaces of the tubes.

As an example of particular tube lengths, in a particular installationaccording to the invention the tubes have a length of 15 meters whilethe conductor 21 which is not connected to any source of current andwhich has the dipole function has a length of 30 meters, and preferablythe arrangement is such that each bath a and 10b has a length of metersproviding the total length of 30 meters for the conductor 21 and ofcourse as the tubes are transported through the apparatus they aremaintained spaced from each other, in the ideal case, by a distance of15 meters, so that in this way the rate of deposition of zinc onto theinner conductor when it acts as a cathode will equal the removal of thecoating therefrom when surrounded by the tube 1 when the inner conductoracts as an anode.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofelectrolytic installations differing from the types described above.

While the invention has been illustrated and described as embodied inelectrolytic process and apparatus, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. 'In a process for electrolytically treating elongated metal tubeswhich are longitudinally advanced one after the other through anelectrolytic bath in which is located an elongated conductor whichextends coaxially through each tube without engaging the latter as eachtube is advanced through the bath and in which there is located a metalelectrode connected electrically with the metal tube through saidelectrolytic bath at a polarity opposite to that of the tube while theelongated conductor is not connected to any source of current, the stepof advancing the metal tubes through the bath one after the other with aspacing therebetween which will provide a covering of the conductor bythe tubes which at a maximum is approximately two thirds of the lengthof the conductor in the electrolytic bath.

2. In a process for electrolytically treating elongated metal tubeswhich are successively advanced longitudinally through an electrolyticbath in which is located an elongated conductor which extends coaxiallythrough the tubes without touching the latter as they are advancedthrough the bath and in which there is an electrode electricallyconnected through said electrolytic bath with each metal tube as itpasses through the bath but of an opposite polarity thereto, the step ofsuccessively advancing said tubes through said bath while maintainingthe distance between the successive tubes substantially equal to thelength of said tubes.

3. In a process for electrolytically depositing on the interior andexterior surfaces of elongated metal tubes a metal coating while passingthe tubes successively through an electrolytic bath in which is locatedan elongated conductor which passes coaxially through the tubes withouttouching the latter as they are advanced through the bath with a metalanode located in the bath and the tubes themselves acting as cathodeswhile the elongated conductor is not connected to any source of current,the step of successively advancing the tubes through the bath in amanner which maintains at all times from one half to one third of theconductor uncovered, so that said conductor will have a dipole functionreceiving metal from said anode while said conductor is uncovered by atube and giving up the metal thus received from the anode to theinterior surface of the tube while the conductor is covered by the tube.

4. In an apparatus for electrolytically treating metal tubes, incombination, elongated electrolytic bath means adapted to contain anelectrolyte through which the tubes to be treated are longitudinallypassed; an elongated electrical conductor carried by said bath means inthe interior of said bath means; means operatively connected to saidbath means for transporting therethrough the metal tubes one after theother and spaced in axial direction from each other through said bathmeans with said conductor passing coaxially through the tubes withouttouching the latter and so that at any instant at least one third of thelength of said electrical conductor in said bath means is uncovered bythe metal tubes; and electrical means for electrically interconnecting asource of direct current only with a metal plate which is located insaid bath and said tubes with opposite polarities therebetween.

'5. In an apparatus for electrolytically treating metal tubes, incombination, elongated electrolytic bath means adapted to contain anelectrolyte through which the tubes to be treated are longitudinallypassed; an elongated electrical conductor carried by said bath means inthe interior of said bath means; means operatively connected to saidbath means for transporting therethrough the metal tubes one after theother and spaced in axial direction from each other through said bathmeans with said conductor passing coaxially through the tubes withouttouching the latter and so that at any instant at least one third of thelength of said electrical conductor in said b-ath means is uncovered bythe metal tubes; electrical means for electrically interconnecting asource of direct current only with a metal plate which is located insaid bath and said tubes with opposite polarities therebetween; and aplurality of resilient, electrically non-conductive, elasticallydeformable plugs carried by and distributed along said conductor foryieldably engaging the interior surface of the metal tubes as they aretransported through the bath to center said conductor in said tubes.

6. In an apparatus for electrolytically depositing metal from a givenplate onto the interior and exterior surface of elongated metal tubes,in combination, elongated bath means adapted to contain an electrolyte;an elongated electrical conductor extending through and carried by saidbath means and being electrically insulated at opposite ends thereof;transporting means for transporting the metal tubes one after the otherand spaced in axial direction from each other through the bath meanswith said conductor located coaxially within and out of contact Withsaid tubes and so that at any instant at least one third of the lengthof said electrical conductor in said bath means is uncovered by themetal tubes; electrical means electrically interconnecting a source ofdirect current only with the tubes and the plate in a manner renderingsaid plate which is in said bath an anode and said tubes a cathode; andsleeve means of the same metal as said plate covering said conductor andalso maintained out of contact with the tubes as they are transportedthrough the bath means.

7. In an apparatus for electrolytically treating metal tubes, incombination elongated bath means adapted to contain an electrolyte aswell as a plate of metal in said electrolyte; an elongated electricalconductor extending through said bath means and being electricallyinsulated at opposite ends thereof; transporting means for transportingthe tubes one after the other and spaced in axial direction from eachother through said bath means with said conductor extending coaxiallythrough but not contacting said tubes and so that at any instant atleast one third of the length of said electrical conductor in said bathmeans is uncovered by the metal tubes; electrical means for electricallyinterconnecting a source of direct current only with said tubes andplate while providing opposite polarities for said tubes and plate,respectively; and a plurality of electrically non-conductive resilient,elastically deformable plugs of frustoconical configuration carried byand distributed along said conductor for slidably engaging the interiorsurface of the tubes as they are transported through the bath means.

8. In an apparatus for electrolytically treating elongated metal tubes,in combination, elongated bath means adapted to contain an electrolyteand a metal plate, said bath means being divided into at least twoidentical units each containing electrolyte and each containing a metalplate; an elongated electrical conductor electrically insulated atopposite ends thereof and passing through said electrolyte in said bathmeans; transporting means for transporting the tubes one after anotherand spaced in axial direction from each other through the bath meanswith said conductor passing coaxially through the tubes withoutcontacting the latter and so that at any instant at least one third ofthe length of said electrical conductor in said bath means is uncoveredby the metal tubes; and electrical means electrically interconnectingonly said tubes and said plates with a source of direct current whileproviding said plates on the one hand and said tubes on the other handwith opposite polarities, respectively.

9. In an apparatus for electrolytically treating elongated metal tubes,in combination, elongated bath means adapted to contain an electrolyteas well as a metal plate, said bath means including an upper electrolytecontainer, a lower reservoir for the electrolyte located beneath saidcontainer, conduit means providing communication between said reservoirand container, pump means for pumping electrolyte from said reservoirinto said container, overflow chambers respectively located before andafter said container for receiving electrolyte which is not retained insaid container, and additional conduits providing communication betweensaid chambers and reservoir for directing to the latter electrolytewhich reaches said chambers; an elongated electrical conductorelectrically insulated at opposite ends thereof and carried by said bathmeans and passing therethrough in said container thereof; transportingmeans for transporting one after the other through said container andspaced in axial direction from each other, said metal tubes with saidconductor passing coaxially through but not contacting said tubes and sothat at any instant at least one third of the length of said electricalconductor in said bath means is uncovered by the metal tubes; andelectrical means interconnecting a source of direct current only withsaid tubes and plate while providing opposite polarities for said tubesand plate, respectively.

10. In an apparatus for electrolytically treating elongated metal tubes,a plurality of bath means arranged one after the other along apredetermined path and respectively adapted to contain differenttreating liquids, an intermediate one of said bath means being adaptedto contain an electrolyte while at least one bath means in advance ofsaid intermediate bath means is adapted to contain a liquid fordegreasing the tubes; an elongated conductor extending through all ofsaid bath means and being composed for the most part of an electricalconductor covered with a layer of insulation, said conductor beinguncovered in the bath which is located in advance of said intermediatebath for degreasing the tubes and said conductor in said intermediatebath which contains electrolyte being insulated from the remainder ofthe conductor; means for advancing the metal tubes successively andspaced in axial direction from each other through the several baths withsaid conductor passing coaxially through the tubes without contactingthe latter and so that at any instant at least one third of saidconductor in said intermediate bath means is uncovered by said tubes;means for providing a source of current for the uncovered conductorportion in the degreaser bath for electrolytically degreasing the tubesas they pass through the latter; and electrical means for connecting thetubes, as they pass through the inter-mediate bath means with a directsource of current which is also connected with a plate in saidintermediate bath means which is provided with a polarity opposite tothat of said tubes as they pass through the intermediate bath meanswhich contains the electrolyte.

11. In an apparatus for electrolytically treating elongated metal tubes,in combination, bath means adapted to contain an electrolyte andcontaining a metal plate in the electrolyte; an elongated electricalconductor extending through the electrolyte of the bath means and beingelectrically insulated at opposite ends thereof; electrically conductivetransporting means located adjacent said bath means for transportingtherethrough one after the other the metal tubes which are to be treatedspaced in axial direction from each other with the conductor passingcoaxially through but being out of contact with the tubes and so that atany instant at least one third of the length of said electricalconductor in said bah means is uncovered by the metal tubes; andelectrical means connected only to said transporting means and to saidplate for electrically interconnecting the transporting means and platewith a source of direct current and for providing said plate and saidtubes through said transporting means with opposite polarities.

12. In an apparatus for electrolytically polishing tubes provided with ametal coating at their exterior and interior surfaces, in combination,electrolytic bath means; a metal plate located in the electrolyte ofsaid bath means; an elongated electrical conductor extending through thebath means in the electrolyte thereof but being electrically insulatedat opposite ends thereof; transporting means for transporting throughthe electrolyte in said bath means metal tubes one after the other withthe conductor extending coaxially through the tubes without contactingthe latter and so that at any instant at least one third of the lengthof said electrical conductor in said bath means is uncovered by themetal tubes; and electrical means operatively connected only to saidtubes and plate for connecting them with a source of direct currentwhile providing them with polarities which cause said tubes to act asthe anodes and said plate to act as a cathode.

References Cited UNITED STATES PATENTS 1,003,799 9/1911 Rodeck 204262,711,993 6/ 1955 Lyon 204-26 2,970,950 2/ 1961 Bahmann 204-26 JOHN H.MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner.

us. or. X.R.

